1. Field of the Invention
The present invention relates to a method of controlling a semi-conductor resistance defining component, and more particularly, to a method and device for adjusting a drive signal to a semi-conductor resistance defining component to thereby control its electrical rsistance.
2. Descirption of the Related Art
Various semi-conductor components are or may be used as controllable resistors, the resistance between two terminals of the component being dependent upon a drive signal applied to the component. Such a component then may be coupled into an electronic circuit such that its resistance controls the characteristics of the circuit. By way of example, a field-effect transistor can be used in an automatic gain control (A.G.C.) amplifier, the drain-source resistance of the field-effect transistor being used as the gain control parameter and this resistance being varied by an AGC signal applied to the gate of the field-effect transistor.
A problem with the above device is that the tolerance on some semi-conductor resistance defining components, some field-effect transistors for example, are sufficiently wide to prevent proper design-time definition of circuits making use of the components. If a one off circuit is being made or if it is to be reproduced only a very few times, then each circuit can be individually set up and the problem of definition is not so significant. Otherwise, attempts have to be made to design out too great a dependency of the circuit characteristics upon the inherent characteristics of its components. If this is not successful, then of course the characteristics will vary from one reproduction of the circuit to another or when the relevant component is replaced.